This invention relates generally to gas burners for residential furnaces and for commercial heating and cooling packaged products and, more particularly, to apparatus for reducing NOX emissions from such devices.
Continued concern about atmospheric pollution has created renewed interest in lowering the emissions of various combustion devices. Of particular concern are nitric oxide (NO) and nitrogen dioxide (NO2) emissions because of their roles in forming ground level smog and acid rain, and in depleting stratospheric ozone. For simplicity, NO and NO2 are often grouped together as NOx. Many jurisdictions have stringent NOx emissions regulations. For example, California limits NOx emissions from gas furnaces to a maximum of 40 ng/J. It is expected that over the coming years, the regulations will become more stringent.
The common mechanism for the formation of NOx in a gas fired furnace is referred to as thermal NOx. In this mechanism, high flame temperatures, generated by the combustion process, result in the formation of NOx. The primary strategy to control NOx formation is to lower the flame temperature. One method is shown in U.S. Pat. No. 4,904,179, wherein a radiant member is inserted in the flame. The member heats up, radiates energy away from the flame and thereby cools the flame down. The disadvantage of this method is that the NOx benefit gained will not be enough to meet possible future regulations. Another method to lower flame temperature is to recirculate flue gas into the flame. The presence of combustion products suppresses flame temperature. One method is achieving this, is described in a preferred embodiment of U.S. Pat. No. 6,071,115. High momentum secondary air jets are injected into the primary fuel-air mixture from the outside, thereby promoting mixing and causing a recirculation of the combustion products into the flame. However, it is difficult to apply this concept to a furnace in a simple, and cost-effective way.
It is therefore an object of the present invention to provide an improved apparatus and method for reducing NOx in a gas burner.
Briefly, in accordance with one aspect of the invention, a tube is inserted into the downstream area of a burner and air is supplied to one end of the tube and emerges at the other end thereof so as to thereby reduce the resulting generation of NOX.
By another aspect of the invention, the tube extends radially inwardly near the end of the burner and then turns to extend substantially along an extension of the burner axis, with the air being discharged at the end of the tube, the position of which is optimized to obtain a desired degree of NOX reduction while maintaining a low noise level.
In the drawing as hereinafter described, a preferred embodiment is depicted; however, various other modifications and alternate constructions can be made thereto without departing from the true spirit and scope of the invention.